The present invention relates to a focusing screen mounting device for use in a single lens reflex camera.
In a camera which is so designed that the focusing screen below the penta-prism can be freely removed through the camera body mounting opening, when the focusing screen is inserted through the opening and set in place, it is always necessary that the focusing surface of the focusing screen be fixed at a position equivalent to that of the image plane on the film. In addition, the focusing screen must be stably mounted so that it cannot be displaced readily by shock or vibration. In the production line manufacture of cameras, the mounting surface, on the body side, of the focusing screen is liable to be affected by dimensional variations of related components and by the variations in assembly of the components. Accordingly, it is difficult to obtain a correct focusing position directly upon assembling the components. Therefore, during assembly of a camera, a so-called "focus adjustment" must generally be carried out by moving the focusing surface of the focusing screen vertically. In order to satisfy the above-described conditions, a number of components and a number of steps of adjustment are required for a conventional focusing screen mounting device.
A conventional focusing screen mounting device of the general type to which the invention pertains is shown in FIG. 1. A focusing screen holder 3 is arranged to allow a focusing screen 2 to abut against the lower surface 1a of a focusing screen supporting frame 1. A leaf spring 5 is secured to a mirror box rear part 6 by a shaft 4 at the rear end portion 3b of the focusing screen holder 3 to ensure that the focusing screen 2 is pushed up by the abutting portion 3a of the focusing screen holder 3. The front end portion 3c of the focusing screen holder 3 is engaged with a cut 8a formed in a stop 8 which is fixedly secured to a mirror box front part 7 to set the focusing screen 2 in place. If the front end portion 3c is disengaged from the stop 8, the focusing screen holder 3 is forced to swing down around the shaft 4 whereby the focusing screen 2 can be removed in the conventional manner.
The focusing screen supporting frame 1 is movable up and down to set the focusing screen 2 at the correct position. However, in the conventional focusing screen mounting device, the leaf spring 5 for pushing up the focusing screen 2 is provided only on one side, and accordingly the focusing screen holder 3 must be made turnable around its front end 3c which is fixed as a result of which a portion other than the abutting portion 3a of the focusing screen holder 3 is brought into contact with the focusing screen 2. That is, the focusing screen 2 is unstably depressed by the focusing screen holder 3.
In order to correct this unstable state, a step of moving the stop 8 vertically with an eccentric dowel 9 or the like is included in the assembling process. This step can be eliminated by making the stop 8 elastic vertically although the number of components is thereby increased, and accordingly not only the cumulative error but also the manufacturing cost is increased. Thus, the latter technique is considered not suitable.
In view of the foregoing, an object of the invention is to provide a focusing screen mounting device having higher stability than the previously-known devices of this type.